Before a person stands on such a scale to be weighed, he must turn the scale on using a switch. This may be a foot-actuated switch on the face end of the scale or it can be done by briefly putting a load on the scale. In the latter case, however, the scale must first be unloaded again without weighing taking place. If the scale is turned on but is still unloaded, that is, still prior to the actual weighing process, then the "zero value" required for evaluation, or in other words, the value to be assigned to the output signal of the weighing cell in the unloaded state, is first ascertained. Then the zero value is displayed, for instance as 0000. Only then can the actual weighing process begin. The zero value is then subtracted from the value ascertained. The difference is converted by the microprocessor and displayed as the weight.
A disadvantage in these known digital scales is that they must first be turned on, and then there must be a waiting period, for instance, one or two seconds long, before a person can weigh himself. On the other hand, the scale must be turned on for zero value determination prior to the weighing, because otherwise the weighing cell and the microprocessor would use up the batteries too fast, if they used current continuously (the weighing cell uses 3 mA, the microprocessor 0.5 to 1 mA, at 3 V).